1. Technical Field
The present disclosure relates to a wheel fastening inspection method which checks whether or not a fastening force when a rotary member is fastened to a turbine shaft is appropriate, a wheel fastening method, a wheel fastening inspection device and a wheel fastening device.
2. Description of the Related Art
A conventional turbocharger is provided with a bearing housing, and a turbine shaft which is rotatably supported to the bearing housing, is provided with a turbine wheel (a turbine impeller) at its one end and is provided with a compressor wheel (a compressor impeller) at its other end. The turbocharger is connected to an engine, rotates the turbine wheel by exhaust gas which is discharged from the engine, and rotates the compressor wheel via the turbine shaft by the rotation of the turbine wheel. As described above, the turbocharger compresses air along with the rotation of the compressor wheel and supercharges the engine.
The turbine shaft has a step portion which is formed closer to the compressor wheel side than a position where a radial bearing is provided. An outer diameter of the step portion is smaller than an outer diameter of the position where the radial bearing is provided. A rotary member such as a thrust collar or an oil thrower, and the compressor wheel are sequentially attached to the turbine shaft up to the step portion with no gap in an axial direction. Finally, a nut is screwed to a shaft end side of the turbine shaft. According to the screwing, an axial force (a fastening force generated by the nut) of the turbine shaft is applied to a contact portion among the step portion, the rotary member and the compressor wheel. The axial force suppresses rotational deviation between the rotary member and the compressor wheel, and the turbine shaft at the time of engine operation. For example, a preset-type torque wrench which can set the fastening torque can be used for fastening the nut.
In the case where the preset-type torque wrench is used for fastening the nut, variation is generated in the axial force which is generated with respect to the fastening torque of the nut. This is caused by individual difference in a coefficient of friction between the rotary member and the compressor wheel which are fastened by the nut. Therefore, an appropriate torque management is required for fastening the nut. Furthermore, for example, in the case or the like where the compressor wheel is attached to the turbine shaft by press fitting, it is necessary to insert the thrust collar and the oil thrower to the turbine shaft with no gap in order to apply a desired axial force to the thrust collar and the oil thrower. Therefore, in this case, an appropriate load management for the press fitting of the compressor wheel (hereinafter, referred to as a press fitting force management) is required for the press fitting of the compressor wheel.
In Japanese Patent Laid-Open Publication No. 2009-228446 (Patent Literature 1), a technique for specifying the axial force is disclosed. In this technique, the turbine shaft has a chamfer portion extending in an axial direction, at a position where the compressor wheel is attached. In addition, a strain gauge is attached to the chamfer portion. The axial force is derived from the strain of the turbine shaft which is measured by the strain gauge. Note that a lead wire of the strain gauge is drawn to the outside through a hole which communicates from the chamfer portion to the shaft end of the turbine shaft.